to make GStreamer to work on the receiving side, port is known since preset
so I need Wireshark to get ip.address, source address of my camera in multicasting mode
to enter in the following CLI command

This will receive de RTSP stream, decode it, re-encode it, and save it to a file. If you knew the camera’s encoding format and handled key frames properly you could do it without the transcoding and save the processing (and battery life).

You could even capture the 4 cameras and combine them in a single file using the compositor.